US 4,759,920 AGranted

Process for the manufacture of disodium phosphate

AssigneeNegev Phosphates Ltd.

InventorsAlexander Iosef, Menachem Bar-On

Life of this patent

Estimating the term…

Loading patent…

Abstract

The present invention relates to a process for the manufacture of disodium phosphate of a high purity without utilizing organic solvents. According to the process, monosodium sulfate is reacted, at a temperature, in the range of 40 to 100 degrees C. with a phosphate constituent selected from phosphate rock, dicalcium phosphate or mixtures thereof, in the presence of phosphoric acid. The common metal impurities, organic matter and fluorides present in the starting phosphate rock are substantially complete eliminated with the solid gypsum or dicalcium phosphate resulted thereto. After separating said solid, the filtrate is treated in two neutralization stages: first by a calcium constituent selected from calcium carbonate, calcium hydroxide or mixtures thereof and separating the formed dicalcium phosphate, followed by a second neutralization with an alkali sodium constituent selected from sodium hydroxide, sodium carbonate and sodium bicarbonate or mixtures thereof at a pH in the range of 8.0 to 9.5. From the resulted filtrate, pure disodium phosphate is obtained by crystallization. The process is characterized by a high recovering of the P.sub.2 O.sub.5 and Na.sub.2 O values, the resulted product being substantially free of chloride ion.

Claims11

Dependent claims

A process for the manufacture of substantially pure disodium phosphate without utilizing organic solvents which comprises the steps of:

(a) reacting in at least two stages, at a temperature between 40.degree. C. and 100.degree. C. monosodium sulfate with a phosphate constituent selected from the group consisting of phosphate rock, dicalcium phosphate and mixtures thereof in the presence of phosphoric acid to form a slurry containing phosphoric acid, monosodium phosphate and calcium sulfate and separating out the formed calcium sulfate to obtain a filtrate containing phosphoric acid and monosodium phosphate, the amount of phosphoric acid being in the range of between 5% and 20% of the total P.sub.2 O.sub.5, the slurry being characterized by the absence of monocalcium phosphate;
(b) neutralizing in two stages the filtrate obtained in step (a) first with a calcium constituent selected from calcium carbonate, calcium hydroxide and mixtures thereof, at a pH in the range of between 4 and 6.5 to obtain a slurry containing dicalcium phosphate and separating out the formed dicalcium phosphate, followed by further neutralizing with an alkali sodium constituent selected from sodium hydroxide, sodium carbonate and sodium bicarbonate or mixtures thereof at a pH in the range of 8.0 to 9.5;
and
(c) crystallizing out from the filtrate formed in step (b) substantially pure hydrated disodium phosphate.

1 more element

Dependencies are inferred from the claim text.